Wednesday, February 18, 2009

Plant toxicity comes up a lot at work. People who are buying a plant often want to know if it's safe for dogs, cats, birds, children, or what have you, and this is something that houseplant books are surprisingly reluctant to cover.

We do have a (cat-specific) list at work, up at the front counter, and I refer to it sometimes, but it's not entirely accurate (it lists Sansevieria trifasciata as safe, when it is not) and is really horribly incomplete.

Sansevieria trifasciata 'Moonglow' or 'Moonshine' (which are possibly the same plant under different names). This species can be lethal to cats.

So I've been trying for some time now to do the research and come up with some kind of actual, useful list to make a blog post about, and/or use at work instead of the list we've got, and this has been frustrating. There will still be a list, eventually: I'm trying as hard as I can. But here's why it's taking longer than it should to come up with:

1. The lists do not agree with one another. One list has a plant as safe, the next list will say it's poisonous. Sometimes this is resolvable, sometimes it's not.

2. The lists are usually very short. It's a rare one that has more than about fifty names on it: there are more than fifty species of plant in the room I'm sitting in right now. So they're extremely limited, and many plants aren't on any list, period.

3. They give almost no indication of how dangerous a plant actually is. Tradescantia zebrina, which plant might, at worst, make your cat throw up or irritate your baby's skin, is sitting there on the same "unsafe" list as Adenium obesum and Nerium oleander, either of which could take down your whole family reuinion. Nerium and Tradescantia are clearly not equivalent safety risks, and yet the lists almost never indicate that some plants are more dangerous than others.

Tradescantia zebrina.

4. There's a lot of guilt by association. Dieffenbachia spp. contain calcium oxalate crystals. Dieffenbachia spp. are ridiculously dangerous. Spathiphyllum spp. also contain calcium oxalate crystals. Therefore Spathiphyllum spp. must also be ridiculously dangerous. Except -- no. As far as I've been able to find in firsthand accounts or in the medical literature, Spathiphyllum spp., if eaten, might make your mouth burn and hurt, but there don't seem to be any actual cases of someone being killed or seriously injured by one. The calcium oxalate crystals, while unpleasant, are clearly not the whole story. This is not to say that association is never useful: it's a pretty reasonable bet that if Maranta leuconeura erythroneura is safe, and Calathea ornata is safe, then Stromanthe sanguinea, which is also in the family Marantaceae, is going to be safe too. But do you want to bet somebody's life on that?

5. The names. Oh, gods, the names. Looking around at the existing on-line lists, I have found:

a. Names which are merely misspelled but otherwise clear ("buddist pine," "cineria"),b. Common and botanical name mismatches ("aralia -- Dizygotheca elegantissima"),c. Names which are so vague as to be completely useless ("evergreen"),d. Names which refer to more than one plant at once -- a common enough pitfall of common names anyway ("zebra plant"),e. Cultivar names being presented as common names ("Florida Beauty"),f. Cultivar names that refer to more than one species (If "Florida Beauty" is on the list, then does that mean that Philodendron 'Florida Beauty' is toxic, or that Dracaena surculosa 'Florida Beauty' is? Or are they both? Or are we talking about some other "Florida Beauty," perhaps Caladium 'Florida Beauty?'),g. Names which are fragmentary ("elaine," "cordatum"),h. Names which are obscure ("monkey plant" -- or is that a typo for "money plant?" And if it's a typo, which "money plant" are they talking about?),i. And names which are just plain wrong ("dracaena palm," "lily spider").

6. And then even the most conscientious of sites will usually make no distinction among the possible victims: either it's poisonous to everything: cats, dogs, people, birds, fish, snakes, and lizards, or it's safe for everything. The odds are good that some plants are toxic to reptiles but not mammals, or toxic to cats but not anything else. None of the lists acknowledge this.

So here's the rant part, specifically for the medical, veterinary, and pet-enthusiast communities:

If you're going to put one of these toxic/non-toxic lists on your website, I beg you to please go to the trouble to, you know, make sure that your lists refer to actual plants. It's not good enough to throw names together at random without differentiating between botanical, common, and cultivar names, or worse yet, putting botanical, common and cultivar names together in new combinations. If you do this, you're making the toxic-plant situation more confusing, and therefore worse.1 If I can't figure out whether Begonias are dangerous or not, given weeks to look at all the on-line lists and the relatively low stakes of having no actual pets or children to worry about, how in the hell do you expect people who do have pets or children to be able to figure it out? Should they just go with whatever website comes up first in the Google search? Flip a coin?

It'd also be nice, in light of the variability of common names,2 if someone would include some pictures with these lists. I may not know "aluminum plant," and I may not know Pilea cadierei, but if one of these is in my house, I'd recognize it:

I will continue to try to piece together a usable list from other lists, anecdotes, inference, and guilt-by-association, but don't count on said list being available anytime very soon. I've been working on it for months already, and have not actually answered most of the questions I set out to answer. So it's slow. Don't hold your breath.

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1 As far as it goes, this is a really good argument for why houseplant owners should make the effort to learn the botanical names for their plants. You don't have to be able to pronounce it, you don't need to be able to spell it, but at the very least you should be able to recognize it if you see it, or know what letters it starts with, or something. Can you imagine calling Poison Control, thinking your pet or child is dying in front of your eyes, and not being able to call the plant s/he just ate anything more specific than "tropical foliage?" Or (to bring back my favorite example) "zebra plant?" ("Okay, sir/ma'am, calm down. Can you tell me which zebra plant you're talking about? There are eleven by that name in the book here.")2 I know someone who had a plant she calls "Polish plant" because it came from a relative originally, and the relative believed that it was from Poland. This was the common name within the family, but of course nobody who wasn't in the family would have known what "Polish plant" was, or had any way to find out. Also the plant turned out to be a Pandanus veitchii, and they're not Polish at all. Not even close, really: veitchii is from Madagascar. (Wikiposedly, anyway.)

13 comments:

Good post. I have posted one of these lists as it is a common question I get asked but I've always been doubtful about them. Humans certainly vary enormously in their allergic / toxic reaction to certain plants. I have never personally had trouble with the sap of Dumb Cane for example, but others may. If you want another rant - I feel the same about the quasi-science around so-called air cleaning houseplants.

Thank you very much for bring up this subject. If it hadn't been for you and this blog I would have bought an Adenium thinking that it was only as poisonous for the cats and I as a pothos. Glad I waited for your write up on that plant. I didn't find Adenium listed on any of the poisonous websites that I looked at.

I think you covered the issue very well, information is definitely lacking/incomplete/erroneous. And for the reptile owner, like me, there are just no way to be sure of what's to avoid exactly. That's why I have strickly insectivore species in wonderful fully planted terrariums, while I keep my larger one that could potentially try to eat foliage, even though it's mostly carnivore/insectivore, with ugly plastic fake plants. Herp keepers just mostly don't agree on anything, like your sources. And the worse part is that generally the information only applies to mammals. If it's possible, while doing your research, please have a thought for herp enthusiats and include information on reptiles whenever it's indicated? :)

Your list will be a valuable contribution, whenever it reaches its definitive state of incompletion.

I've encountered the same problems in researching hardy landscape plants for clients who are anxious parents. The lists lump together hollies (whose berries are generally emetic, hence Ilex vomitoria) and death camas (Zigadenus sp, the consumption of one bulb of which can be fatal.)

But I've seen estimates that about a third of all plant species are toxic to humans, at least in part.

There are over 50,000 species in cultivation in the state of Connecticut alone.

So such a list, if carefully researched, should serve as a sort of "America's Most Wanted"---well, make that "Least Wanted". I'm concerned that people may take such a list to indicate that plants not on the list are safe. Zach's rule of thumb is sensible.

I can't tell you how many times customers freaked out over some mildly irritating plant like it was going to wipe out their neighborhood. Then one of my kids at a bit of datura and I freaked out. A good list would be very useful, but I think it would be impossible to cover everything. Still, it will be better than what I have been able to find.

In South East Asia, we have a plant called Dumb Cane, dieffenbachia. I used the grow them in Singapore. The sap makes one very itchy, and parents warn children not to put them in their mouth, otherwise they get dumb.

I too have found this a frustrating predicament. It is a question that often appears on vivarium forums.

As has already been mentioned, one of the problems with generating such a list is that there are plants which pose health haards (from mild to severe) for humans but which pose none to animals and vice versa.

And again, as others have mentioned, there is the simple fact that what may be harmful to one animal may not be for another. Trying to create one sweeping list is rather ludicrous. (Brings to mind a goat the parents of a friend of mine owned. Stupid thing drank half a large can of turpentine. Wouldn't you know other than going off its feed for a day the dumb thing was just fine?)

Then, in addition to level of toxicity, don't forget that not ALL parts of a plant may be cause for concern. Just look at potatoes -- the tuber is just fine to eat, but don't eat any other part of the plant. Or rhubarb, whose leaf stalks are the edible portion.

Some of the lists out there would seriously make one question the wisdom of ever setting foot outside for fear of coming in contact with a "dangerous" plant

There are better ways to approach this:On-line - http://maxshouse.com/Poisonous_Plants_IDX_Common.htmorhttp://www.ansci.cornell.edu/plants/

Although the best reference I've ever seen (limited tropicals though) was at the library of my local Botanical Garden:Toxic Plants of North America, George E. Burrows & Ronald J. Tyrl, Iowa State University Press, Ames, 2001

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